f:ajax doesn't obey the 'execute' attribute but always sends all the fields in a form. Mojarra does, however, only process the listed fields as supposed. However, excess fields shouldn't be sent because it increases request size.
<h:inputText id="field1" />
<h:inputText id="field1x" />
<f:ajax execute="field1" />
On button click, both fields are sent (but only field1 would be processed).
See for further info: http://stackoverflow.com/questions/3889894/jsf-2-0-why-does-fajax-send-all-the-form-fields-and-not-only-those-marked-with
PrimeFaces has recently implemented this, would be great to have this in the spec.
Must have feature for JSF 2.3. This really shouldn't be that hard, should it?
An implementation duplicate: JAVASERVERFACES-1841